Apomorphine (APO) is receiving renewed interest in its pharmacology not only due to its usefulness in Parkinson's disease but also in the treatment of other neurological and mental diseases (both idiopathic and drug-induced) which normally respond to treatment with dopamine antagonists. Recent reports in the literature and results in our own laboratory suggest very strongly that APO possesses the ability to stimulate presynaptic dopamine receptors and that chronic administration of the drug results in the induction of postsynaptic dopamine receptor supersensitivity for a period of up to 12 days after cessation of that chronic treatment. We propose an indepth study of changes in dopamine receptor sensitivity via analysis of time and dose response relationships of APO-induced stereotypic behavior and 3H-spiroperidol binding in rats that have been treated chronicallywith APO and subsequently subjected to withdrawal from the drug. These analysis will be compared to parallel experiments conducted with another aporphine (M-N-propylnorapomorphine), and indirect-acting dopamine agonist (dextroamphetamine) and a dopamine antagonist (spiroperidol). We will also attempt to study the effects of long-term APO administration upon cessation of chronic APO treatment. We will also investigate the suggestion that lithium will prevent development of supersensitive dopamine receptors by administration to animals upon cessation of chronic APO treatment. Establishment of an "agonist induced supersensitivity of dopamine receptors" could have clinical implications in the treatment of neurological and mental diseases with dopamine agonists or antagonists.